1. Field of the Invention
The present invention relates to an outlet nozzle for centrifuge rotors and, more particularly, to an outlet nozzle having an improved structure for facilitating installation within and removal from a centrifuge rotor wall.
2. Description of the Prior Art
Centrifugal machines of a nozzle type typically include a rotor defining a separating chamber containing a stack of separating discs for effecting a two-fraction separation of a feed slurry. The feed slurry is separated into a heavy discharge slurry, or underflow fraction, which is delivered outside the rotor by a plurality of nozzles supported within the outer wall of the rotor. A light fraction or separated liquid is removed from the rotor by overflow from the top end of the machine.
To effect proper separation of the feed slurry, it is necessary to rotate the rotor within a conventional centrifugal machine at a high angular speed, typically around 3,100 rotations per minute (RPM). The high rotational speed of the rotor creates sufficient centrifugal force to separate the heavy discharge slurry outwardly to the nozzles supported within the outer wall of the rotor. The centrifugal force also necessitates that the nozzles be adequately secured to the outer wall to ensure that the nozzles remain therein during rotation of the rotor.
One arrangement for securing a centrifuge nozzle to a rotor wall is disclosed in U.S. Pat. No. 2,695,748 to Millard which is incorporated by reference herein. A plurality of such nozzles are mounted at regularly spaced intervals about the periphery of the rotor wall. More particularly, the rotor wall is provided with a plurality of cylindrical bores for receiving the nozzles wherein the axis of each bore is radially disposed with respect to the axis of the rotor. Means are provided for detachably securing each nozzle within the wall wherein the means consists of a lug which is formed integral with the body of the nozzle. The rotor wall is machined to provide an arcuate groove or recess within each cylindrical bore wherein the groove is dimensioned to accommodate the lug. The groove is semi-circular, and its ends open into a cavity formed within the outer surface of the rotor wall adjacent the cylindrical bore.
When the nozzle is positioned within the cylindrical bore such that the lug is disposed within the groove, the nozzle is securely locked to the rotor wall. When the nozzle is turned approximately 180.degree. from this locked position, the lug is brought into registration with the cavity such that the body may be retracted from the rotor wall. A slot is provided on the end of the nozzle for engagement by a suitable turning tool, such as a screwdriver, to facilitate rotation of the nozzle.
During prolonged operation of the centrifuge, the nozzles often become plugged with discharge slurry thereby requiring the cleaning of the discharge orifices in the nozzles. Additionally, it is common for the nozzles to wear or erode over time due to extended contact with the abrasive discharge slurry. In order to facilitate cleaning of the plug discharge orifices, and replacement of worn nozzles, it is well known in the prior art to detachably mount the nozzles in the outer wall of the rotor. Before the Millard nozzle, the prior art means of attachment often required access to the interior of the rotor in order to install or remove the nozzles.
While the above mentioned Millard nozzle has addressed the task of installing new nozzles, there remains a need for improved means of removing nozzles from a rotor wall. While the Millard nozzle facilitates use of a screwdriver to impart torque and rotational movement to the nozzle, no means are provided for applying a force acting radially outwardly from the rotor along the axis of the nozzle to remove the nozzle from its receiving bore. During operation, the nozzles usually become bonded to the rotor wall by solid or liquid materials passing through the centrifuge, such that the nozzles are essentially welded in place. Additionally, sealing means, such as O-rings, provided between the nozzle and the rotor wall resist forces applied in attempts to remove the nozzles from the cylindrical bores within the rotor wall. Attempts to remove the nozzles often leads to the use of screwdrivers or other tools to pry the nozzle out of the rotor wall. The use of these tools against the rotor wall in attempt to gain leverage can result in considerable damage to the rotor wall. In extreme cases, the nozzles are bonded to the rotor wall to such an extent that metal must be welded to the top end of the nozzle so it may be pulled out by applying radially outwardly acting force.
Accordingly, there is a need for a centrifuge nozzle having an improved structure to facilitate installation within and removal from a rotor wall. There is a further need for a hand tool adapted for engaging the centrifuge nozzle to assist a user in installing and removing the nozzle from the rotor wall.